EBV is a human gamma-herpesvirus that infects over 90% of the adult population worldwide. In combination with known and unknown cofactors, especially immunosuppression, EBV infection constitutes a high carcinogenic risk. EBV has been classified by the World Health Organization as a class I human carcinogen because of its causal association with Burkitt's lymphoma, nasopharyngeal carcinoma, about 50% of all Hodgkin's lymphoma, gastric carcinoma, angiocentric T/NK lymphoma, and lymphoproliferative disorders of the immunosuppressed. EBV is responsible for about 1% of all human cancers, worldwide. The oncogenic potential of EBV is readily demonstrated in vitro by its capacity to immortalize primary B-lymphocytes in culture, and in vivo by its ability to drive infected B-cells into aggressive lymphoblastic lymphomas in immunocompromised hosts.
EBV, like other herpesviruses, has a latent and lytic replication cycle. While the EBV lytic cycle is essential for viral transmission and increases risk of EBV-associated malignancy, it is the latent viral infection that is oncogenic. The latent virus expresses a limited set of viral genes that stimulate cellular proliferation and survival. Clinically available inhibitors of herpesvirus DNA polymerases, including variants of acyclovir (e.g. ganciclovir) and phosphonoacetic acid (e.g. foscarnet) have at least partial inhibitory activity against EBV lytic replication. However, none of the available herpesvirus antivirals are effective at blocking the virus from progressing to a latent infection or eliminating latent infection. Primary infections with EBV can evoke a robust, sometimes debilitating immune response referred to as infectious mononucleosis (IM). Despite this robust immune reaction, the virus efficiently establishes latent infection in B-lymphocytes, where the virus can reside in long-lived memory B-cells. In some circumstances, latent infection can also be established in T-lymphocytes and epithelial cells. During latency, the virus does not produce infectious particles, and viral gene expression is limited to a subset of transcripts with growth-transforming and anti-apoptotic functions that contribute to EBV carcinogenesis. Thus, no existing anti-viral drug or immunological response can block the establishment of an EBV latent infection, which has the potential to drive lymphoid and epithelial cell oncogenic growth transformation.
Numerous studies have demonstrated that Epstein-Barr Nuclear Antigen 1 (EBNA1) is an ideal target for elimination of latent infection and treatment of EBV-associated disease. In one aspect, EBNA1 is expressed in all EBV-positive tumors. In another aspect, EBNA1 is required for immortalization of primary B-lymphocytes and for the stable maintenance of the EBV genome in latently infected cells. In yet another aspect, genetic disruption of EBNA1 blocks the ability of EBV to immortalize primary human B-lymphocytes and causes loss of cell viability in previously established EBV-positive cell lines. In yet another aspect, biochemical disruption of EBNA1 folding blocks the establishment of EBV latent infection. HSP90 inhibitors cause the selective killing of EBV+ B-cells and block lymphomagenesis in mouse models. In yet another aspect. EBNA1 is a non-cellular viral oncoprotein that is functionally and structurally well characterized. The three-dimensional structure of EBNA1 bound to its cognate DNA sequence has been solved by X-ray crystallography. Analysis of the DNA binding domain reveals that EBNA1 protein is druggable, with several deep pockets and channels within the DNA binding domain that are predicted to disrupt DNA binding when bound to small molecules. In yet another aspect, targeting a non-self viral-encoded protein for inhibition mitigates the potential risk of inherent toxicity. EBNA1 has a unique structural fold that is distinct from all known cellular DNA binding and replication proteins. In yet another aspect, the EBNA1 DNA binding function is essential for all known EBNA1 functions, including genome maintenance, DNA replication, transcription regulation, and host-cell survival. These studies demonstrate that EBNA1-DNA binding domain is a validated target for inhibition of EBV-latent infection and treatment of EBV-associated malignancies.
EBV plays a causative role in the tumorigenesis for a number of cancers including nasopharyngeal carcinoma, gastric carcinomas, non-hodgkin lymphoma (anaplastic large-cell lymphoma, angioimmunoblastic T-cell lymphoma, hepatosplenic T-cell lymphoma. B-cell lymphoma. Burkitt's lymphoma, reticuloendotheliosis, reticulosis, microglioma, diffuse large B-cell lymphoma, extranodal T/NK lymphoma/angiocentric lymphoma, follicular lymphoma, immunoblastic lymphoma, mucosa-associated lymphatic tissue lymphoma, B-cell chronic lymphocytic leukemia, mantle cell lymphoma, mediastinal large B cell lymphoma, lymphoplasmactic lymphoma, nodal marginal zone B cell lymphoma, splenic marginal zone lymphoma, intravascular large B-cell lymphoma, primary effusion lymphoma, lyphomatoid granulomatosis, angioimmunoblastic lymphadenopathy), leiomyosarcomas, X-linked lymphoproliferative disease, post-transplant lymphoproliferative disorders, Hodgkin's lymphoma and breast cancer. An inhibitor of EBNA1 would change current clinical practice and be valuable for therapeutic treatment of EBV-associated diseases. Currently, nucleoside analogues (aciclovir, ganciclovir, foscarnet) can be used to treat lytic EBV infection and pathologies related to lytic EBV infection. However, these general antiviral drugs are not specific for lytic EBV infection, and carry the risk of severe adverse effects.
EBV infection and EBNA1 have also been implicated in infectious mononucleosis, chronic fatigue syndrome (CFS), multiple sclerosis, systemic lupus erythematosus, and rheumatoid arthritis. Treatment with compounds that prevent EBV infection and/or prevent lytic EBV infection and/or prevent latent EBV infection and/or inhibit EBNA1 would provide therapeutic relief to patients suffering from these diseases. To date, however, no effective specific treatments exist for lytic EBV infection and/or for pathologies related to lytic EBV infection. Further, to date, no effective treatments exist for latent EBV infection and/or pathologies related to latent EBV infection. Further, no effective treatments exist for the treatment of diseases associated with EBNA1.
There is a thus long felt need for novel compounds and methods using the same, which are useful for treating EBNA1 infection and/or diseases associated with EBNA1. Such treatments should be useful for the treatment of subjects afflicted with diseases and conditions associated with EBV infection, and/or subjects that are refractory to current treatments for infectious mononucleosis, chronic fatigue syndrome, multiple sclerosis, systemic lupus erythematosus and/or rheumatoid arthritis. The present invention addresses these needs.